The invention relates to a control circuit between a port of a microprocessor and an actuator in a motor vehicle and to a method of maintaining the momentary state of an actuator controlled by a microprocessor during a dip in the supply voltage.
Actuators are increasingly controlled by microprocessors in modern motor vehicles. During the starting procedure of the engine in a motor vehicle, the vehicle supply voltage dips down to +3 volts. With such voltage dips, microprocessor systems are generally put into the reset state. In that case, the connections or ports are switched as high-impedance inputs (tristate condition) and the function currently being executed is terminated. To prevent this, the microprocessor system, including an auxiliary circuit, can be buffered with a capacitor.
German Patent DE 197 20 191 C1 discloses connecting a buffer circuit between the output of a microprocessor and an actuator in a motor vehicle. There, the buffer circuit has a comparison circuit which, when a predetermined voltage level is reached, switches over between a high level and a low level, which is applied to the control device. In addition, the buffer circuit has an energy store in the form of a buffer capacitor. Due to the fact that the energy store is arranged between the output of the microprocessor and the high-impedance input of the comparison circuit enables a function to be maintained with relatively little power. It is thus possible for the energy store used to be a capacitor of SMD design. As a drawback, however, such a buffer circuit is associated with high circuit complexity and consequently higher costs.
It is accordingly an object of the invention to provide a proper solution for the above-mentioned disadvantages of the heretofore-known devices and methods of this general type and to maintain the operation of an actuator controlled by a microprocessor, using little additional circuit complexity, even when the microprocessor has changed to the reset state as a result of a dip in the supply voltage.
With the foregoing and other objects in view there is provided, in accordance with the invention, a control circuit connected between a control port of a microprocessor and an actuator in a motor vehicle, comprising:
a control stage having
a terminal connection connected to an actuator terminal associated with an actuator in a motor vehicle and connected to an electrical system in the motor vehicle for a voltage supply to the control stage;
a control connection connected to a control port of a microprocessor for applying a low level to the control stage from the microprocessor in special cases; and
an output for outputting a control signal to control the actuator in dependence on a voltage level at the terminal connection and the control connection; and
a driver stage connected to the control stage for amplifying the control signal.
The inventive control of an actuator in a motor vehicle is particularly suitable for functions such as the starter, wipers, rear-window heater, seat heater, interior lighting, turn signal lights and the like, which are usually controlled via the port of a microcontroller.
A control circuit is connected between the port of a microcontroller and the actuator to be controlled. The control circuit has a control stage which is electrically connected to that terminal of the electrical system in the motor vehicle that is associated with the actuator to be controlled, e.g. the starter terminal or the turn indicator terminal. The respective terminal is generally referred to herein as the actuator terminal. The output signal from the control stage is amplified in the driver stage, integrated in the control circuit, in accordance with the requirements of the respective actuator and is used to control the actuator. A microprocessor is also electrically connected to the control stage, but performs only overriding checking and diagnostic functions.
Moving the primary control function from the microprocessor to the control circuit in conjunction with the appropriate actuator terminal makes it an easy matter to maintain operation of the actuator irrespective of the supply voltage for the microprocessor.
In accordance with an added feature of the invention, the control stage further comprises a transistor having a transistor input, and a voltage divider connecting the transistor input to the terminal connection and to the control connection.
In accordance with an additional feature of the invention, the voltage divider is designed such that, in normal operation, when a terminal voltage is applied to the actuator terminal, a resultant voltage level at the control connection is recognized as a high level by the microprocessor and the transistor switches on.
In accordance with another feature of the invention, a decoupling diode is connected in a forward direction between the terminal connection and the voltage divider.
In accordance with a further feature of the invention, a bleed resistor connects the terminal connection to ground.
In accordance with again a further feature of the invention, a diagnostic line connects the driver stage to a diagnostic port of the microprocessor.
With the above and other objects in view there is also provided, in accordance with the invention, a method of maintaining a momentary state of an actuator controlled by a microprocessor during a dip in a supply voltage. The method comprises the following steps, to be performed in dependence on a normal state of the system or a special state, e.g., when the supply voltage dips below a given threshold voltage:
in normal operation, controlling an actuator with a control circuit supplied with voltage via an actuator terminal associated with the actuator; and thereby
outputting a control signal controlling the actuator with a control stage integrated in the control circuit; and
amplifying the control signal in a driver stage integrated in the control circuit;
in special cases, inhibiting the control stage to prevent output of the control signal by outputting a low level at a control port of the microprocessor; and
in normal operation, processing checking and diagnostic functions with the microprocessor.
In accordance with again an added feature of the invention, in special cases, the control port of the microprocessor is switched as an output and a low level is applied to a control connection of the control stage.
In accordance with again another feature of the invention, in normal operation, the control port of the microprocessor is switched as an input and the voltage level at the control connection of the control stage is read into the microprocessor via the input.
In accordance with a concomitant feature of the invention, the voltage level at the output of the driver stage is read into the microprocessor via a diagnostic line and a diagnostic port; the microprocessor compares the voltage levels read in at the control port and at the diagnostic port; and if the voltage levels do not match, a fault function is recognized, the control port is switched as an output, and the low level is applied to the control connection of the control stage. vehicle via a terminal connection 3. The output signal from the control stage 2xe2x80x94referred to as the control signal belowxe2x80x94is amplified in a driver stage 5 and used to control a starter 6. When the ignition switch is closed, that is to say during the whole starting procedure of the engine, the starter terminal 4 is at a terminal voltage of usually 12 volts. A voltage divider comprising resistors R2, R3 and R4 in the control stage 2 uses this terminal voltage to set the voltage at the input of a transistor T1 such that the transistor is turned on. The transistor T1 can be a bipolar npn transistor or an n-channel field-effect transistor FET. To provide the current level required to control the starter 6, the control signal is amplified in a driver stage 5. Such driver stages are known in the art and they are usually transistor-driver circuits with current limitation.
A bleed resistor R1, via which the terminal connection 3 of the control stage 2 is connected to ground, prevents the transistor T1 from being turned on as a result of leakage currents when the ignition switch is open, that is to say when the starting procedure of the engine is not activated. These leakage currents can be the result, for example, of contact resistances being reduced owing to moisture.
A control port 10 of a microprocessor xcexcP connected as a microcontroller 11 is also connected to the input of the transistor T1 via a control connection 12 of the control stage.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a control circuit between a port of a microprocessor and an actuator and method of maintaining the momentary state of an actuator during a dip in the supply voltage, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawing.